1. Technical Field
The present disclosure relates to projection lens systems and, particularly, to a projection lens systems with a long back focal length.
2. Description of Related Art
Projection lens systems generally include at least two lens groups for focusing light rays reflected from a digital mirror device (DMD) on a screen. One of the at least two lens groups moves in relative to the other lens group to adjust a focal length of the projection lens system. However, when the projection lens system is designed with a lower aberration, a back focal length of the projection lens system is very short. Therefore, there is not enough room for positioning optical elements, such as DMD, in the range of the back focal length.
Therefore, it is desirable to provide a projection lens system which can overcome the limitations described above.